Investigating Quinclorac Binding to Human Serum Albumin using Spectroscopy and Molecular Docking

Authors

• Le Nguyen, University of Arkansas - Fort SmithFollow
• L. Hicks, University of Arkansas - Fort SmithFollow
• L. Jodoin, University of Arkansas - Fort SmithFollow
• S. Carby, University of Arkansas - Fort SmithFollow
• D. S. Sanford, University of Arkansas - Fort SmithFollow
• D. Benavides, University of Arkansas - Fort Smith
• A. Mishra, University of Arkansas - Fort SmithFollow
• R. Yadav, University of Arkansas - Fort SmithFollow

Keywords

HSA, Quinclorac, Tryptophan Fluorescence Quenching, Site Marker Displacement

Abstract

Human serum albumin (HSA) is the most abundant plasma protein and serves as a major transporter and reservoir for a wide range of endogenous ligands, including fatty acids, heme, bilirubin, prostaglandins, and metal ions, as well as numerous exogenous compounds, such as pharmaceuticals. HSA is a 66 kDa monomeric, multidomain protein containing two principal ligand-binding sites, Sudlow sites I and II. Sudlow site I contains Trp214, the sole tryptophan residue in HSA, whose intrinsic fluorescence provides a sensitive probe for studying ligand–protein interactions.

In this study, the interaction between HSA and the persistent organochlorine herbicide quinclorac (QNC) was investigated using steady-state fluorescence spectroscopy and molecular docking. The binding of QNC to HSA is characterized by concentration-dependent quenching of HSA's intrinsic tryptophan fluorescence, indicating QNC binding to HSA. Quantitative analysis revealed a high affinity of QNC for HSA, with ~ 1 μM dissociation constant (K_d). Temperature-dependent fluorescence quenching experiments indicate a static quenching mechanism. Moreover, a competitive displacement assay using site-specific markers identified Sudlow site I as the primary binding site for QNC in HSA. Induced-fit docking further demonstrated that QNC is accommodated and stabilized by polar interactions, π-stacking, and/or hydrophobic interactions within the Sudlow I binding pocket. Together, these results provide a biochemical and molecular understanding of how QNC, a persistent pesticide, binds to HSA.

Recommended Citation

Nguyen, Le; Hicks, L.; Jodoin, L.; Carby, S.; Sanford, D. S.; Benavides, D.; Mishra, A.; and Yadav, R. (2026) "Investigating Quinclorac Binding to Human Serum Albumin using Spectroscopy and Molecular Docking," Journal of the Arkansas Academy of Science: Vol. 79, Article 22.

Available at: https://scholarworks.uark.edu/jaas/vol79/iss1/22